Snapchat is definitely not in the same age and situation than pets.com. Look how long it took Yahoo to be forced to sell... If Twitter doesn't start growing soon, it'll be in a similar situation within 24 months.
If the table turns for Snapchat and does not grow, they would force the CEO to step down within a year, then give the new CEO 2 years to show results. If they don't want to sell, then they would replace the second CEO within 18 months.
Of course, this is pure speculation and considering similar companies in hard situations. You should definitely read THE HARD THING ABOUT HARD THINGS by Ben Horowitz.